2006 Infiniti G35 Car shakes sporadically

I have a G35 with aftermarket parts on it. It's stillen supercharged with full exhaust and MB rims. I purchased it with only 12500 miles. The tires were dryrotted and unevenly worn. I kept hearing a slight "rubbing/rotational" noise in the front left, that seemed to get worse on right turns. I recently replaced the tires with 245/45/18 yokohamas (original on this wheel was 235/45/18), had balance and alignment done. At speeds above 60MPH, the car would sporadically bounce, and the steering wheel would have a slight shake to it. I had my mechanic (he's my friend as well) recheck the balance, all good. He didn't think it was a bearing, since it only had 20K miles on it. He also thought I was crazy and hearing things, because he couldn't hear what I was hearing. I took it for a long drive over a weekend and at high speeds (around 80MPH) the entire chassis shook, especially when breaking. Thought maybe a caliper or rotors, so I replaced pads (needed), rotors but the calipers were fine. Shaking was less, but still there. The rubbing sound was still there. I checked the front wheels for sounds, and noticed the front left was making a clicking sound. I took it to the dealer to have them test drive it, and they thought I was crazy as well. That night, I took the front left wheel off, and the bearing was bad. Very loud clicking noise when I spun the hub assembly. I replaced it. Rebalanced the tires at a local shop since the steering wheel still vibrated. Upon getting the car back, took it for a test drive. At 70MPH, the car (seemed from rear end) shook violently. Slowed to 35, went away- back to 65, shook again. Seemed the rear wheels were going to fall off. Pulled over on highway, checked wheel, started backup and drove back to shop. They testdrove it, took the wheels back off (I couldn't see what work they did), remounted the wheels and said shaking was from road. Impossible. That shaking was so violent it sounded like a helicopter and felt like people were shaking the car. It was very dangerous. I didn't believe them, but when I took the car back, it ran perfectly. Maybe they over/under torqued the wheels, forgot to put the hub rings back on? Either way, once I got it back, No sounds, no vibration, no shaking. Drove it over the next -3 weeks for over 500 miles, all was good. On the way back home from a long drive (250mile round trip), a slight body/chassis shake came back. It's getting progressively worse. The steering wheel does not shake, but the chassis does, and it's again sporadic. I purchased new hub centric rings as one of the old ones had a crack in it. I plan to check the front right bearing and rear bearings. The rear bearings are tough because I am not able to spin the wheel easily, even in neutral. (I don't have a lift, only stands) All the suspension components look good. Beyond this, I dont' know what to check. I hate to keep putting money into it but the shaking is really annoying and I'm afraid it will just get worse and cause more damage to other car components. Yesterday it was raining here and the shaking was worse than usual. It's still not shaking as bad as it did before with the bad front-left bearing, but I definitely notice it. I don't understand what's going on. I know how the car feels and sounds when everything is working because for 500 miles, it was a perfectly smooth ride, with new tires and breaks. No shake at all when I break. Otherwise, the car runs perfectly. Any help would be greatly appreciated.